The relatively high dielectric constant and breakdown field strength of tantalum oxide (herein generally TaO.sub.x, x.about.2.5) make thin film TaO.sub.x potentially useful for integrated circuit applications. However, before TaO.sub.x -based dielectric material can be used in production devices, some properties of the material have to be improved. Among these are leakage current which, at least for some IC applications, desirably is reduced over typical prior art values, and breakdown voltage, which desirably is raised.
Two approaches have dominated the efforts to improve the dielectric properties, namely, post-deposition annealing, and incorporation of one or more further metal oxides such as Al.sub.2 O.sub.2, TiO.sub.2, WO.sub..sub.3, SiO.sub.2 or ZrO.sub.2 into the film. The former requires relatively high temperatures, and may lead to crystallization of the TaO.sub.x, a deleterious change. In any case, post-deposition annealing to date has yielded only marginal improvements in leakage current and breakdown voltage.
The latter approach to date also has not yielded the desired improvements in dielectric properties.
Representative of prior efforts are H. Fujikawa et al., J. Applied Physics, Vol. 75 (5), p. 2538 (1994), and K. Nomura et al., J. Electrochemical Soc., Vol. 134, p. 924 (1987). The former reports magnetron sputter deposition of Ta.sub.2 O.sub.5 plus 2 other oxides (e.g., Al.sub.2 O.sub.3 +ZrO.sub.2) in Ar+O.sub.2. The latter reports RF sputter deposition of TaO.sub.x +Al.sub.2 O.sub.3 in Ar+O.sub.2.
See also J. H. Thomas, J. Applied Physics, Vol. 45 (12), p. 5349 (1974), which reports results on the study of defects in anodic Ta.sub.2 O.sub.5 formed on N.sub.2 -doped Ta films. U.S. Pat. No. 4,038,167 discloses formation of a thin film capacitor by a method that comprises RF sputtering a film of Ta oxide in an O.sub.2 --N.sub.2 inert gas atmosphere.
In view of the high dielectric constant and other advantageous properties of TaO.sub.x, it would be desirable to have available a TaO.sub.x -based dielectric film that can have relatively low leakage current and relatively high breakdown voltage. This application discloses such a film, and a method of making the film.